This invention relates to magnetically suspended vehicles in general and more particularly to an improved magnetic system for use in such vehicles, which magnetic system reduces braking losses.
Various systems have been developed for the contactless magnetic suspension and guidance of vehicles. Vehicles of this nature are being designed to reach speeds of over 300 km/hr. Basically two different types of guidance principles are known and use in such systems. In one of these, referred to as the "electromagnetic" guidance principle, magnetic attractive forces are used. In such a system forces between electromagnets attached to both sides of the vehicle and ferromagnetic rail members on the track line are used to generate the necessary forces. In such a system the excitation of the electromagnets must be controllable so that their distance from the rail members can be maintained approximately constant. Another system, which does not require such control, utilizes what is referred to as the "electrodynamic" guidance principle. In such a system magnetic repulsion forces produced by the interaction of magnets attached to the vehicle moving over highly conductive but nonferromagnetic rails or slabs and inducing eddy currents therein are utilized. However, the required field strength of the generally uncontrolled electromagnets used in such an electrodynamic system is quite a bit larger than that of electromagnets used in electromagnetic guidance systems. Because of this the use of super-conducting magnets becomes particularly advantageous particularly since their weight is small compared to that of corresponding normally conducting magnets.
A number of embodiments of electrodynamic suspension and guidance arrangements are known and are disclosed in U.S. Pat. No. 3,470,828. Typically these include a plurality of vehicle magnetic loops arranged on both sides of the vehicle one behind the other in the direction of travel. These vehicle magnet loops interact with corresponding track loops or rails. Individual magnet loops associated with vehicles are elongated and of an approximately rectangular shape so that their end faces situated next to each other can be brought close together. Super-conducting magnets with an elongated coil structure in the travel direction and which are rectangular or only slightly rounded at their end faces are preferably employed as disclosed in U.S. Pat. No. 3,717,103. This design follows from the theory of electrodynamic suspension above a conducting plate. According to this theory the ratio of the lifting force developed to the braking force of such a system is particularly favorable for elongated magnets particularly at high operating velocity, such as velocities in the vicinity of 500 km/hr. Small magnets on the other hand produce a strong skin effect, i.e., when small magnets are used the currents which are necessary in the conducting track loops or rails to develop the necessary lifting forces, at these speeds, are strongly directed from the interior of the track to the track surface and thereby produce larger braking losses.
Furthermore, as taught in the above noted U.S. Pat. No. 3,470,828 it is particularly advantageous if the polarity of each two magnets arranged one behind the other in the travel direction and adjacent to each other is different. Such an alternating polarity results in a large magnetic field gradient between each two magnets and leads to large lifting forces.
However, despite these various measures, as the vehicle velocity increases, braking forces increase. In view of this, the need for an improved system which has lower braking losses at high vehicle velocities becomes evident.